See https://github.com/gentoo/gentoo-docker-images/pull/71 Among other things, the lack of a Docker image for stage3-systemd will almost invariable result in the failure of some Travis CI builds that need both systemd and Gentoo to run.
Fixed in https://github.com/gentoo/gentoo-docker-images/commit/072a818cdfcd831d88927855cfe1979c6b628995 . Tagging Alexy for sign-off and close.